The present invention relates to a method for the diagnosis of a three-way catalytic converter for an internal combustion engine using the voltage signal of a downstream binary lambda sensor.
With the diagnosis of catalytic converters the problem exists that reversible damage occurs due to sulfur poisoning, and irreversible damage of the function of the catalytic converter occurs due to deterioration. Both lead to the reduction of the pollutant conversion such that a conversion that may no longer be sufficient is indicated. However, in the case of reversible damage, the reduction of the pollutant conversion can be reversed.
A method for the determination of the deterioration condition of a storage catalytic converter is described in patent specification DE 103 18 214 B4. The entire reduction of the storage capacity of the catalytic converter is initially established, then the reduction of the storage capacity due to sulfur is calculated by means of a thionation model in consideration of a predetermined sulfur content of the fuel, and in a final step the difference of the entire reduction and of the reversible reduction due to sulfur is formed. This difference corresponds to the irreversible reduction of the storage capacity of the catalytic converter, and is finally compared to a predetermined maximum value.
A catalytic converter diagnostic method is known from patent specification DE 198 44 178 A1, which, in a first method step, performs a regeneration attempt for removing any reversible damage of the functionality, checks the functionality after a completed regeneration attempt, and finally assesses the functionality of the catalytic converted on the basis of this test. Thus, the reversible damage is eliminated in this method such that ultimately only the irreversible damage is considered in the assessment of the catalytic converter.
Furthermore, a method for the diagnosis of a storage catalytic converter is described in the patent specification DE 103 02 700 A1. According to this method the storage catalytic converter is operated in a storage and regeneration mode, and differentiations are made between a reversible and an irreversible damage of the storage catalytic converter in dependency of the storage characteristics and the regeneration time. Accordingly, with low storage characteristics and a long regeneration time, thionation is assumed, while with low storage characteristics and a short regeneration time, a thermal deterioration is diagnosed.
In this regard the task of the invention is to provide a further improved method for the diagnosis of a three-way catalytic converter, which allows an accurate differentiation of damage possibly occurring. Further, the performance of the diagnosis method should not cause any additional emissions.